Since Ampère’s day we have learned at all events, that an electric current means the flow of electrons, either from atom to atom, or passing between the atoms, along conductors. In 1920, Lord Kelvin came to the conclusion that at the absolute zero resistance of metals must be infinitely great, the degrees of dissociation of the electron being, he supposed, nil at the zero hour. If any free electrons remained, he believed they would lose their power of motion, condensing like a vapor upon the metal atoms and freezing fast to them (to borrow a phrase from Kamerlingh-Onnes). The experiments of the celebrated Holland physicist show that the resistance of metals decreases with lowering of temperature, and would probably become nil at the absolute zero with employment of a perfectly pure platinum wire. If this is true, then would a current of electricity, once set up in a conductor, continue forever? FOOTNOTES: [9] _Philosophical Transactions_, Page 127, 1832; First Series, Article 10. [10] One of the first electrical experimenters to devise the instrument known as a “galvanometer” was Professor Schweigger, of Halle. There are now eight or more varieties of this instrument (or apparatus) in use. It enables the investigator to measure extremely minute electrodynamic actions, or the very weakest intensity of an electric current, as well as to detect its presence or direction, usually by the deflection of a magnetic needle. [11] Maxwell, Clerk, “On Action at a Distance,” (_Scientific Papers_, Vol. II, Page 317). [12] The scientific papers of Cavendish were published (in 1879) under the title, “The Electrical Researches of the Hon. Henry Cavendish,” edited by Clerk Maxwell. Cavendish anticipated many later investigations of British and Continental writers, including Ohm’s law—i. e., the proportionality between the electromotive force and the current in the same conductor; and anticipated also Faraday’s discovery of the specific inductive capacity of different substances, even measuring its numerical value in several substances. He had also arrived at the conceptions of electrical capacity and of “potential.” [13] See _Die Naturwissenschaften_ (Berlin), January 28, 1921. CHAPTER 4 THEORIES OF ELECTRICITY The science of electricity is based upon observation of those phenomena of attraction and repulsion which are comprehended under the term _electrostatics_. Statical electricity, so named from a Greek word (statikos), which means “causing to stand (or stay),”—also called _frictional electricity_—is the electricity of stationary charges caused by rubbing together unlike bodies, such as glass and silk (noted in Chapter II). In such cases equal and opposite charges of electricity are always produced. The term _statical electricity_ applies properly, however, to the electricity of all stationary charges, however produced.